The present invention relates generally to optoelectronic interconnect modules for fiber optic communications. The present invention relates more specifically to an optoelectronic interconnect module enabling an optical transmitting or receiving semiconductor die to be mounted to a substrate with an optical axis perpendicular to an optical ferrule mounted to the optoelectronic interconnect module.
Ultrafast optoelectronic transmitters are utilized in data communications systems wherein optical beams are modulated with electronic binary data pulses. The electronic pulses are conveyed by means of metallic conductors to a light-emitting semiconductor device, the modulated output of which may be transmitted over optical media (i.e., fiber optic cables).
Optoelectronic interconnect modules or optical subassemblies may be configured for direct mounting to a circuit substrate or a printed circuit board within the host system. In this arrangement, contact pins extend from the module and are typically soldered directly to contact points on the printed circuit board. The module is usually mounted near the edge of the printed circuit board such that the optical end of the module will protrude through a slot in an adjacent metal faceplate that may be mounted to the metal chassis of the host system.
A transceiver module includes provisions for connecting the module to an optical transfer medium such as a fiber optic cable. A typical arrangement, common to 1xc3x979 modules, is to provide a transceiver module having an SC-duplex fiber optic connector receptacle integrally formed at the optical end of the module. The SC-duplex receptacle is configured to receive an SC-duplex connector in order to couple a pair of optical fibers to the optoelectronic interconnect module. A first optical fiber carries optical signals transmitted by the module, while a second optical fiber carries optical signals to be received by the module.
Ultrafast optoelectronic transceivers are capable of transmitting serial bit streams at rates above 10 Gbps. At these high data rates, electronic components and circuitry within the module are prone to generate undesired emissions and create electromagnetic interference with the surrounding equipment. Therefore, care must be taken to prevent spurious emissions from escaping from the module housing and disrupting the operation of nearby devices. Furthermore, electrical connections should be planar or straight to minimize signal distortion.
With reference to FIG. 1, a first embodiment of a prior art optoelectronic interconnect module is presented. The optoelectronic transceiver module 10 is inserted within the host chassis 12. The module 10 includes a metallic or metallized connector clip having a first prong 14 and a second prong 15 for receiving and retaining a fiber optic connector. Aligned concentrically within the connector clip 14, 15 is an optical subassembly. The optical subassembly includes an optical housing 16, optical lens 24, an annular mounting surface 32, an alignment ring 34, and an optoelectronic package 26. The external end of the optical housing 16 defines a ferrule bore 18 configured to receive a fiber optic connector ferrule 20 which aligns the optical fiber 22 carried within the ferrule 20 with the optoelectronic device contained within the optoelectronic package 26.
The optoelectonic package 26 is externally comprised of a metal cover 28, an optical window 29, and a base 30. The base 30 and cover 28 are both formed of metal and are joined by a conductive interface allowing the optoelectronic package 26 to be maintained at a controlled electrical potential. An insulating substrate 36 is provided within the optical package on the upper surface of the base. An optoelectronic and electronic semiconductor die 38 is mounted to the insulating substrate 36.
A plurality of signal pins extend through the base 30 and are wire-bonded to the optoelectronic and electronic semiconductor die 38, which is mounted to the insulating substrate 36. The signal pins 40, 42, 44 provide signal, voltage, ground to the optoelectronic and electronic semiconductor die 38 contained within the optoelectronic package 26. The signal and voltage pins 40, 42 are insulated from the base 30 by glass sleeves 46 disposed between the pins and the base. The ground pin 44 is connected to the base 30 by a weld joint 48.
With reference to FIG. 2, a second embodiment of a prior art optoelectronic interconnect module 50 is presented. An optoelectronic semiconductor die 52 is bonded parallel to the end surface 70 of an optical fiber 54 within an optical ferrule 56. The optoelectronic interconnect module housing 56 is constructed of an insulator and secured to a ceramic substrate 58. Electronic components 60 that interface with the optoelectronic interconnect module 50 are also attached to the ceramic substrate 58. Interconnect wires 62 provide an electrical connection between the electronic components 60 and the optoelectronic semiconductor die substrate 52. If the optoelectronic interconnect module 50 is functioning as a transmitter, optical radiation 66 emitted by the semiconductor die 52 passes through an optical lens or ball lens 68 in order to be properly focused on the end 70 of the optical filament or fiber 54. Similarly, if the optoelectronic interconnect module 50 is functioning as a receiver, optical radiation emitted from the end 70 of the optical fiber 54 passes through the ball lens 68 in order to be properly focused upon the semiconductor die 52.
As can be seen in the second embodiment of the prior art concept shown in FIG. 2, the semiconductor die 52 is mounted axially in-line to the ferrule 56 and perpendicular to the substrate 58, necessitating the connecting wires 62 to be bent about an angle 72 in order to connect with the electronic components 60. The resulting bend 72 in the connecting wires 62 produces undesired signal distortion. Furthermore, the bend 72 in the connecting wires 62 increases production costs and decreases reliability of the optoelectronic interconnect module 50.
The bend in connecting wires, which is basic to the electrical interconnection of both the referenced prior arts embodiments shown in FIGS. 1 and 2, poses basic limitations for ultra-fast optoelectronic transceiver performance. As compared to a planar or straight electrical interconnect counterpart, the bent interconnection:
increases production cost
decreases reliability
increases signal distortion
The cause of the signal distortion is explained in the following manner:
As the rate of data transmission increases, the connecting wires 62 providing electronic interconnection between the semiconductor die 52 and the electronic components 60 on the substrate 58 to which the module housing 56 is attached become a significant portion of signaling wavelength. In this operating regime, the connecting wires 62 behave as transmission lines with some impedance (Z).
With reference to FIG. 3, a schematic representation of the electronic interconnect between the semiconductor die contained within the optoelectronic housing and the electronic components is presented. As the interconnect impedance (Z) deviates from the system impedance (Z), frequency-dependent signal reflections will occur at the impedance mismatch, causing signal distortion. This signal distortion is the primary physical shortcoming in prior art designs that the present invention corrects by providing a planar interconnect that establishes an electronic connection of controlled impedance.
Accordingly, there is a need for an optoelectronic interconnect module that provides planar electronic interconnections and enables optical semiconductor die to be mounted in the same geometric plane as ancillary high speed electronic components within the transceiver assembly.
The objective of the present invention is to enable a semiconductor die, which transmits or receives optical signals, to be directly mounted to a circuit substrate mounting other components, using planarized or straight inter-connecting wires and fiber optic transmission filaments.
A consequence of the objective of the present invention is to minimize signal distortion.
Another consequence of the objective of the present invention is to prevent unintentional radiation.
A further consequence of the objective of the present invention is to reduce production costs.
According to the present invention, an optoelectronic interconnect module is provided having a housing with a first aperture on a side for receiving an optical ferrule, and a second aperture on a bottom for receiving an optical package housing semiconductor die. A mirror is mounted within the housing at an angle for reflecting optical transmissions between the first and second apertures. A first optical lens is mounted between the first aperture and the mirror, and a second optical lens is mounted between the second aperture and the mirror.